Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds real value by enumerating returned fields (E.164 form, activation state, routing object id) since there is no output schema, but it says nothing about pagination, result caps, or the per_page caveat beyond what the schema states.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

A single front-loaded sentence that names the resource then the returned shape; no filler. The trailing 'GET /numbers' is a minor, low-value addition but does not dilute the content.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, describing the returned field set is exactly the right compensating information, and the schema fully carries the filters. The remaining gap is that nothing tells an agent how to interpret an empty result or the interaction with activation state filtering across plans, but that is a minor omission for a list tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and each of the 8 filter parameters is documented in the schema, including the paging caveat and the site_id cross-reference. The description adds no parameter meaning beyond the schema, so the baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('List the phone numbers of the account') and enumerates the fields returned, which makes the tool's output scope concrete. It doesn't explicitly contrast itself with the sibling placetel_get_number (single-number lookup) or placetel_list_number_profiles, so sibling differentiation is only implied.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

No guidance on when to use this versus placetel_get_number for one number or placetel_list_number_profiles for profiles. The only narrowing hint ('GET /numbers') is an endpoint reference, not a usage rule, and the filter conditions live entirely in the schema.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.